U.S. patent application number 10/009759 was filed with the patent office on 2002-12-26 for perfluoroelastomers having a low glass transition temperature and method of making them.
Invention is credited to Gool, Guy Van, Grootaert, Werner M.A., Hare, Erik D, Hintzer, Klaus, Marz, Franz, Worm, Allan T.
Application Number | 20020198345 10/009759 |
Document ID | / |
Family ID | 32295729 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020198345 |
Kind Code |
A1 |
Grootaert, Werner M.A. ; et
al. |
December 26, 2002 |
Perfluoroelastomers having a low glass transition temperature and
method of making them
Abstract
A method of making a curable fluoroelastomer is disclosed. The
method comprises the steps of preemulsifying at least one
perfluorovinylether in water, and copolymerizing the preemulsified
perfluorovinylether with a gaseous fluorinated monomer in the
presence of a cure site monomer. The method provides a
fluoroelastomer having a glass transition temperature of less than
-10.degree. C. Also disclosed is a fluoroelastomer that consists
essentially of a perfluorovinylether of formula (I) as defined
below, a cure site component, perfluoromethylvinylether, and
tetrafluoroethylene and/or chlorotrifluoroethylene. 1.
Inventors: |
Grootaert, Werner M.A.;
(Oakdale, MN) ; Hintzer, Klaus; (Woodbury, MN)
; Marz, Franz; (Burgkirchen, DE) ; Gool, Guy
Van; (Melsele, DE) ; Worm, Allan T; (North
Saint Paul, BE) ; Hare, Erik D; (St. Paul,
MN) |
Correspondence
Address: |
James V Lilly
Office of Intellectual Property Counsel
3M Innovative properties Company
P O Box 33427
St. Paul
MN
55133-3427
US
|
Family ID: |
32295729 |
Appl. No.: |
10/009759 |
Filed: |
December 11, 2001 |
PCT Filed: |
January 31, 2001 |
PCT NO: |
PCT/US01/03195 |
Current U.S.
Class: |
526/247 ;
526/249; 526/250 |
Current CPC
Class: |
C08F 14/26 20130101;
C08F 14/26 20130101; C08F 214/262 20130101; C08F 2/16 20130101 |
Class at
Publication: |
526/247 ;
526/249; 526/250 |
International
Class: |
C08F 116/12 |
Claims
1. A method of making a curable fluoroelastomer comprising the
steps of: pre-eniulsifying one or more liquid perfluorovinylethers
in water with the aid of a fluorinated emulsifier to obtain an
aqueous emulsion, said liquid perfluorovinylether corresponding to
the formula:
CF.sub.2.dbd.CF(O(CF.sub.2).sub.n).sub.m(OCF.sub.2).sub.xOR.sub.f
(I) wherein n represents an integer of 1 to 6, m represents an
integer of 1 to 3, x represents an integer of 0 to 3, with the
proviso that the sum of x and m is at least 3 when n equals 1 and
R.sub.f represents a perfluoroalkyl group having 1 to 6 carbon
atoms; and copolymerizing said pre-emulsified liquid
perfluorovinylethers with a gaseous fluorinated monomer selected
from the group consisting of tetrafluoroethylene,
chlorotrifluoroethylene, perfluorovinylinethyl ether and mixtures
thereof in the presence of one or more cure site component; the
amount of said one or more liquid perfluorovinyl ethers being
sufficient so as to obtain a fluoroelastomer having a glass
transition temperature of less than -10.degree. C.
2. A method according to claim I wherein the total amount of said
liquid perfluorovinyl ether, the amount of said gaseous fluorinated
monomer and the amount of said cure site component are selected
such so as to produce a fluoroelastomer that contains at least 50
mol % of a repeating unit derived from said gaseous fluorinated
monomer, from 15 to 45 mol % of a repeating unit derived from said
liquid perfluorovinylether and from 0.1 to 5 mol % of cure sites
derived from said cure site component.
3. A method according to claim I wherein said liquid perfluorovinyl
ether is copolymerized with tetrafluoroethylene and/or
chlorotrifluoroethylene and perfluoromethylvinyl ether in the
presence of a cure site component such that the resulting
fluoroelastomer contains at least 50 mol % of repeating units
derived from tetrafluoroethylene and/or chlorotrifluoroethylene, 1
to 15 mol % of repeating units derived from perfluoromethylvinyl
ether, between 15 and 35 mol % of repeating units derived from said
liquid perfluorovinyl ether and between 0.1 and 5 mol % of cure
sites.
4. A method according to claim 1 wherein said liquid perfluorovinyl
ether is represented by the formula
CF.sub.2.dbd.CFO(CF.sub.2).sub.pOCF.sub.3 wherein p is 2 or 3.
5. A method according to claim 1 wherein said cure site component
is comprises a halogen capable of participation in a peroxide cure
reaction.
6. A method according to claim 5 wherein said cure site component
is a fluorinated monomer comprising a halogen capable of
participation in a peroxide cure reaction.
7. A method according to any of claims 1 to 4 wherein said cure
site component is a fluorinated monomer having one or more nitrile
groups.
8. A method according to claim 6 or 7 wherein said fluorinated
monomer is a vinyl ether.
9. A method according to claim I wherein said cure site component
comprises a liquid cure site monomer and wherein said liquid cure
site monomer is pre-emulsified with the aid of a fluorinated
emulsifier in water and said pre-emulsified liquid cure site
component is then copolymerized with said gaseous fluorinated
monomer and said pre-emulsified liquid perfluorovinyl ether.
10. A method according to claim 9 wherein said liquid cure site
monomer and said liquid perfluorovinyl ether are pre-emulsified to
obtain an aqueous emulsion comprising the liquid cure site monomer
and the liquid perfluorovinyl ether.
11. A curable fluoroelastomer consisting essentially of 15 to 35
mol % of repeating units derived from one or more liquid
perfluorovinyl ethers of formula (I), 0.1 to 5 mol %, at least 50
mol % of units derived from a gaseous fluorinated monomer selected
from the group consisting of tetrafluoroethylene,
chlorotrifluoroethylene, perfluorovinylimethyl ether and mixtures
thereof and 0 to 10 mol % of repeating units derived from further
perfluorinated monomers other than said liquid perfluorovinyl ether
and said gaseous fluorinated monomer.
12. A curable fluoroelastomer consisting essentially of: (a) 15 to
35 mol % of repeating units derived from one or more liquid
perfluorovinyl ethers of formula (I), (b) 0.1 to 5 mol % of cure
site component, (c) 1 to 15 mol % of repeating units derived from
perfluoromethylvinylether, (d) at least 50 mole % of repeating
units-derived from tetrafluoroethylene and/or
chlorotrifluoroethylene; and the sum of(a)+(b)+(c)+(d) adding up to
100 mol %.
13. A curable fluoroelastomer according to claim 11 or 12 wherein
said liquid perfluorovinyl ether is represented by the formula
CF.sub.2.dbd.CFO(CF.sub.2).sub.pOCF.sub.3 wherein p is 2 or 3.
14. A curable fluoroelastomer composition comprising (i) a curable
fluoroelastoiner according to claims 11 to 13 and (ii) a curative
and/or a catalyst.
15. A fluoroelastomer article obtainable by curing a curable
fluoroelastomer composition as defined in claim 14.
16. Method of making a curable fluoroelastomer including one or
more cure sites derived from a liquid cure site monomer, comprising
the steps of pre-emulsifying one or more liquid cure site monomers
in water with the aid of a fluorinated emulsifier to obtain an
aqueous emulsion and copolymerizing the pre-emulsified liquid cure
site monomers with one or more gaseous fluorinated monomers.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to fluoroelastomers that have
a low glass transition temperature, i.e. that have a glass
transition temperature of -10.degree. C. or less and to a method of
making them. More particularly, the present invention relates to
(per)fluoroelastomers that are derived from a fluorinated olefin
selected from the group consisting of tetrafluoroethylene,
chlorotrifluoroethylene, perfluoromethyl vinyl ether and mixtures
thereof and one or more liquid perfluorovinylethers. 2.
BACKGROUND OF THE INVENTION
[0002] Fluoroelastomers and in particular perfluoroelastomers such
as those described in "Modern Fluoropolymers", edited by John
Scheirs, Wiley Science 1997, offer excellent protection against
high service temperatures and are resistant to a wide variety of
chemical reagents. Fluoroelastomers are generally divided in two
main classes, namely those that are based on vinylidene fluoride
(VF2) and those that do not contain VF2 and are based on
tetrafluoroethylene (TFE) and/or chlorotrifluoroethylene (CTFE) and
perfluoromethyl vinylether (PMVE). Fluoroelastomers based on VF2
are disclosed in for example U.S. Pat. No. 5,696,216, U.S. Pat. No.
5,639,838, U.S. Pat. No. 4,418,186 and U.S. Pat. No. 4,619,983. VF2
based fluoroelastomers generally have a lower chemical and heat
resistance as compared to fluoroelastomers that are based on
TFE/CTFE and PMVE. Unfortunately, these latter fluoroelastomers
have the disadvantage that the glass transition temperature is
somewhat high thereby limiting their low temperature performance.
Various approaches are known to lower the T.sub.g of these
fluoroelastomers.
[0003] Barney et al (J. Poly. Sci. A-1, 8, 1091-1098 (1970))
described the addition of Krytox.RTM. perfluoroalkyl polyether oils
to lower T.sub.g. However, these plasticizers can be extracted by
solvents over time.
[0004] Uschold (U.S. Pat. No. 4,513,128) describes
perfluoro-terpolymers consisting of tetrafluoroethylene,
perfluoromethyl vinylether and at least 3 mol % of long chain
vinylethers 1
[0005] n=3-30. The long-chain vinylether lowers the T.sub.g
significantly, however the incorporation is rather difficult.
Therefore, one has to run the polymerization in perhalogenated
solvents (e.g. R 113) or in aqueous emulsion polymerization in the
presence of fluorinated alcohols. The disadvantages of these
systems are: the use of perhalogenated solvents (e.g. R 113) is
often critical due to environmental concerns and the removal of the
fluorinated alcohols is often very difficult because they act as
swelling agents.
[0006] U.S. Pat. No. 4,766,190 discloses the aqueous emulsion
polymerization of tetrafluoroethylene, hexafluoropropylene and
perfluorovinylethers of the formula
CF.sub.2.dbd.CFO--(CF.sub.2CFXO).sub.- m--R.sub.f wherein X is F or
CF.sub.3, m is 1 to 50 and R.sub.f is a perfluoroalkyl group.
Although the disclosed fluoroelastomers have a low T.sub.g, their
method of making involves polymerization times of up to 28 hours
(see Example 1), making their manufacturing expensive.
[0007] U.S. Pat. No. 5,891,974 describes the aqueous emulsion
polymerization of tetrafluoroethylene and perfluorovinylethers
[0008]
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.2(OCF.sub.2).sub.nOCF.sub.3
n=1-5. However, the polymerization process disclosed to make these
fluoroelastomers, is again in the order of 30 hours.
[0009] WO 99/48939 discloses peroxide curable perfluoroelastomers
of a perfluoro-olefin, a perfluorovinyl ether, including a
perfluoroalkyl vinyl ether and a halogen containing cure site. The
perfluoroelastomers are produced by an aqueous emulsion
polymerization.
[0010] It would now be desirable to improve the process of making
fluoroelastomers that are based on TFE and/or CTFE and a
perfluorovinylether, in particular to make the process less
cumbersome and more cost effective. It would further be desirable
to obtain fluoroelastomers with beneficial properties such as good
cure properties and good mechanical and physical properties when
cured. 3.
SUMMARY OF THE INVENTION
[0011] The present invention provides a process of making a curable
fluoroelastomer comprising the steps of:
[0012] pre-emulsifying one or more liquid perfluorovinylethers in
water with the aid of a fluorinated emulsifier to obtain an aqueous
emulsion, said liquid perfluorovinylether corresponding to the
formula:
[0013]
CF.sub.2.dbd.CF(O(CF.sub.2).sub.n).sub.m(OCF.sub.2).sub.xOR.sub.f
(1)
[0014] wherein n represents an integer of 1 to 6, In represents an
integer of 1 to 3, x represents an integer of 0 to 3, with the
proviso that the sum of x and m is at least 3 when n equals 1 and
R.sub.f represents a perfluoroalkyl group having 1 to 6 carbon
atoms; and
[0015] copolymerizing said pre-emulsified liquid
perfluorovinylethers with a gaseous fluorinated monomer selected
from the group consisting of tetrafluoroethylene,
chlorotrifluoroethylene, perfluoromethylvinyl ether and mixtures
thereof in the presence of one or more cure site component;
[0016] the amount of said one or more liquid perfluorovinyl ethers
being sufficient so as to obtain a fluoroelastomer having a glass
transition temperature of less than -10.degree. C.
[0017] It has been found that the above process allows for a
substantially faster polymerization reaction than the
polymerization processes disclosed in the prior art. In particular,
it was found that by preemulsifying the liquid perfluorovinyl ether
of the above formula prior to its copolymerization with the other
comonomers, the polymerization time can be reduced and the
incorporation is high. Fluoroelastomers having a low T.sub.g and
desirable physical and mechanical properties can thus be obtained
in a convenient and cost effective way.
[0018] By the term "liquid perfluorovinylether" is meant that the
perfluorovinylether is generally present as a liquid at ambient
conditions of temperature and pressure, i.e. at a temperature of
20.degree. C. and a pressure of 1 atm. By the term "pre-emulsified"
in connection with the present invention is meant that the
perfluorovinylether is emulsified in water with the aid of the
fluorinated emulsifier prior to polymerization of the liquid
perfluorovinylether. The term aqueous emulsion is to be understood
as a liquid emulsified in water that generally has a milky
appearance generally having a settling time of at least 1 hour.
Such settliing time is generally achieved using a non-telogenic
fluorinated emulsifier other than a fluorinated polyether
emulsifier. By the term "boiling point" in connection with the
present invention is meant a boiling point under ambient
conditions, i.e. at a pressure of about 1 atm. By the term
"gaseous" in connection with the present invention is meant that
the respective compounds are present as a gas under ambient
conditions of temperature and pressure, i.e. at a temperature of
about 20.degree. C. and a pressure of about 1 atm.
[0019] Particularly preferred fluoroelastomers that can be obtained
with the process of the invention are those that consist
essentially of 15 to 45 mol %, preferably 20-35 mol % of repeating
units derived from one or more liquid perfluorovinlyl ethers of
formula (1), 0 1 to 5 mol %, preferably 0.2 to 3 mol % especially
preferred 0.4-2 mol % of cure site component, at least 50 mol % of
units derived from a gaseous fluorinated monomer selected from the
group consisting of tetrafluoroethylene, chlorotrifluoroethylene,
perfluoromethylvinyl ether and mixtures thereof and 0 to 10 mol %
of repeating units derived from further perfluorinated monomers
other than said liquid perfluorovinyl ether and said gaseous
fluorinated monomer.
[0020] An especially preferred fluoroelastomer that can be obtained
with the process of the invention consists essentially of:
[0021] (a) 15 to 35 mol % of repeating units derived from one or
more liquid perfluorovinyl ethers of formula (1),
[0022] (b) 0.1 to 5 mol % of cure site component,
[0023] (c) 1 to 15 mol % of repeating units derived from
perfluoromethylvinylether,
[0024] (d) at least 50 mole % of repeating units derived from
tetrafluoroethylene and/or chlorotrifluoroethylene; and the sum
of(a)+(b)+(c)+(d) adding up to 100 mol %. These polymers often show
better product properties (e.g., lower hardness and lower
compression sets) when compared to polymers having the same or very
similar glass transition points but having no
perfluoromethylvinylether incorporated.
[0025] The invention also provides a curable fluoroelastomer
composition comprising the preferred and especially preferred
fluoroelastomers set forth above and to a shaped fluoroelastomer
article that can be obtained by curing such curable
fluoroelastoiner compositions. 4.
DETAILED DESCRIPTION
[0026] The perfluorovinyl ethers used in the process of the
invention correspond to the general formula:
[0027]
CF.sub.2.dbd.CF(O(CF.sub.2).sub.n).sub.m(OCF.sub.2).sub.xOR.sub.f
[0028] wherein n represents an integer of 1 to 6, m represents an
integer of 1 to 3, x represents an integer of 0 to 3, with the
proviso that the sum of x and m is at least 3 when n equals 1 and
R.sub.f represents a perfluoroalkyl group having 1 to 6 carbon
atoms.
[0029] R.sub.f in the above formula can be a linear, branched or
cyclic perfluoroalkyl group. Examples of R.sub.f groups include
CF.sub.3--, CF.sub.3CF.sub.2--, CF.sub.3CF.sub.2CF.sub.2-- and
CF.sub.3CF(CF.sub.3)--. The perfluorovinyl ether is used as a
comonoiner to achieve a pertluoroelastomer with a low Tg, i.e. a Tg
of -10.degree. C. or less, preferably -15.degree. C. or less, more
preferably -18.degree. C. or less. To achieve the desired Tg, a
sufficient amount of the perfluoiovinyl ether should be used.
Generally, this amount will be such so as to obtain a
fluoroelastomer containing between 10 mol % and 50 mol % of
repeating units derived from the perfluorovinyl ether, preferably
between 15 mol % and 45 mol %, most preferably between 20 mol % and
35 mol %.
[0030] A preferred class of perfluorovinyl ether for use in the
process of the invention corresponds to the following formula:
[0031] CF.sub.2.dbd.CF--O--(CF.sub.2).sub.p--OR.sub.f
[0032] wherein R.sub.f has the same meaning as defined above and
wherein p is an integer of 2 to 4. Examples of such monomers
include those wherein p is 2 or 3 and wherein R.sub.f represents
perfluoromethyl.
[0033] Further perfluorovinyl ethers that can be used in the
process of this invention include those that correspond to the
formula:
[0034] CF.sub.2.dbd.CF--(OCF.sub.2CF.sub.2).sub.rOR.sub.f
[0035] wherein R.sub.f has the same meaning as defined above and
wherein r is an integer of 1 to 3.
[0036] In accordance with the process of the present invention, the
liquid perfluorovinylether of formula (I) is emulsified in water
with the aid of a fluorinated emulsifier prior to its
copolymerization with the gaseous fluorinated monomers. The
pre-emulsificatioii oftlie liquid fluorinated monomer preferably
results in an emulsion having monomer droplets of a diameter of 1
.mu.m or more, typically it is expected the range of 1 to 20 .mu.m.
The aqueous emulsion should preferably have a pot life (settling
time) of at least 1 hour, more preferably at least 3 hours. The pot
life or settling time is defined as the time required for 10% by
weight of the monomer droplets to settle or separate out of the
aqueouis emulsion.
[0037] Aqueous emulsions of the liquid perfluorovinylether of
formula (I) can conveniently be obtained by suitable emulsification
equipment such as for example a dispersing device such as
Ultra-Turrax. The stirring rates should be sufficiently high to
achieve the desired degree of emulsification and stability.
Generally, stirring rates of 24 000 rpm or more can be employed.
According to indication of the supplier of the Ultra-Turrax device,
the resulting emulsions would have a droplet size of 1 to 10 .mu.m.
Air is preferably excluded during the emulsification.
[0038] Fluorinated emulsifiers for preparing the aqueous emulsion
of the liquid perfluorovinylether of formula (I) are preferably
non-telogenic emulsifiers. Examples of fluorinated emulsifiers
include salts, in particular ammonium salts of linear or branched
perfluoro alkyl carboxylic and sulphonic acids having 6 to 11
carbon atoms in the alkyl chain. It was found that salts of
branched perfluoroalkyl carboxylic and sulphonic acids are more
effective than their linear counter parts. Specific examples
include perfluorooctanoic acid ammonium salt (APFOA) and
C.sub.8F.sub.17SO.sub.3Li. Commercially available fluorinated
emulsifiers that can be used include C.sub.8F.sub.17SO.sub.3Li
available as FT 208 from Bayer AG, and
C.sub.8F.sub.17SO.sub.2N(C.sub.2H.sub.5)CH.s- ub.2COOK available
from 3M as FC 128.
[0039] However, APFOA is the preferred emulsifier as it can be more
readily removed from the polymerization product at the end of
polymerization. Typically, APFOA is very volatile and decomposes at
temperatures of 180.degree. C. or more leading to volatile
products. Therefore, APFOA type of emulsifiers can be easily
removed during work-up of the fluoropolymers.
[0040] The pot life of the aqueous emulsion of the liquid
perfluorovinyl ether of formula (I) can be increased by increasing
the pH. For example, with APFOA, the pot life can be increased to
50 hours or more at a pH of 7 or more. Typically, the pH of the
aqueous emulsion can be increased by adding ammonia or alkali metal
hydroxides.
[0041] The amount of fluorinated emulsifier used to emulsify the
liquid perfluorovinyl ethers of formula (I) is generally between
0.1 and 1% by weight based on the weight of the water phase.
Although higher amounts of emulsifier can be used, they will not
necessarily lead to a significant increased pot life of the aqueous
emulsion. Further, the use of high amounts of emulsifier is not
preferred because the emulsifier generally needs to be removed
after polymerization, making the process less effective.
[0042] The aqueous emulsion of the liquid perfluorovinyl ether of
formula (I) may include a mixture of liquid perfluorovinyl ethers
of formula (I) and may further comprise other monomers such as
other poorly water soluble and liquid monomers. Additional
emulsifier may be added and if added, they are preferably identical
to the emulsifier(s) used to pre- emulsify the liquid
perfluorovinyl ether of formula (I). Advantageously, APFOA is used
in the emulsification of the liquid perfluorovinyl ether of formula
(I) and in the subsequent aqueous emulsion polymerization.
[0043] The pre-emulsification of the liquid perfluorovinyl ether of
formula (I) may proceed in a separate vessel from the
polymerization vessel, in the polymerization vessel itself prior to
commencing the polymerization or in the monomer supply line to the
polymerization vessel.
[0044] According to a particular embodiment of the process of the
invention, the aqueous emulsion of the perfluorovinyl ether of
formula (I) is mixed with tetrafluoroethylelle (TFE),
chlorotrifluoroethylene (CTFE), perfluoromethylvinylether (PMVE) or
mixtures thereof and with one or more cure site component. The
amount of TFE, CTFE and/or PMVE is generally such that a
fluoroelastomer is obtained that contains at least 50 mol % of
repeating units derived from these monomers. Preferably, the amount
of units derived from TFE and/or CTFE is at least 50 mol % and the
amount of repeating units derived from PMVE is between I and 15 mol
%. The amount of liquid perfluorovinyl ether of formula (I) is
generally such that the resulting fluoroelastomer will have between
15 and 45 mol %, preferably between 20 and 35 mol % of repeating
units derived therefrom. Further emulsifier may be added in the
polymerization. The polymerization is generally conducted in the
presence of an inorganic free radical initiator system such as
ammonium persulfate or potassium permanganate. The polymerization
reaction may further include other components such as chain
transfer agents and complexing agents. The polymerization is
generally carried out at a temperature between 10.degree. C. and
100.degree. C., preferably between 30.degree. C. and 80.degree. C.
The polymerization pressure is usually between 3 bar and 20 bar,
preferably between 5 bar and 15 bar.
[0045] The polymerization reaction may involve further fluorinated
monomers other than the gaseous fluorinated monomer, cure site
monomers and liquid perfluorovinyl ether of formula (I). Such
further fluorinated monomers include for example
hexafluoropropylelle.
[0046] The aqueous emulsion polymerization can be carried out
continuously under steady-state conditions in which, for example,
the aqueous emulsion of the perfluorovinyl ether of formula (I) and
the other monomers, water, emulsifiers, buffers and catalysts are
fed continuously to a stirred reactor under optimum pressure and
temperature conditions while the resulting emulsion or suspension
is removed continuously. An alternative technique is batch or
semibatch polymerization by feeding the ingredients into a stirred
reactor and allowing them to react at a set temperature for a
specified length of time or by charging ingredients into the
reactor and feeding the monomers into the reactor to maintain a
constant pressure until a desired amount of polymer is formed.
[0047] The free-radical polymerization process can also be carried
out in the presence of a perfluorosulfinate and an oxidizing agent
to improve the processability of the resulting perfluoroelastomer
composition. Such oxidizing agents are water soluble and capable of
converting the sulfinate to a sulfonyl moiety. The produced
sulfonyl radical is believed to eliminate SO.sub.2 and form a
fluorinated radical that initiates the polymerization of the
ethylenically unsaturated monomers. A number of useful oxidizing
agents are known as taught in U.S. Pat. No. 5,285,002 and U.S. Pat.
No. 5,639,837. Representative examples of such useful oxidizing
agents are sodium, potassium, and ammonium persulfates,
perphosphates, perborates, percarbonates, bromates, chlorates and
hypochilorites. Othie- useful oxidizing agents include cerium IV
compounds such as (NH.sub.4).sub.2Ce(NO.sub.3).sub.6. The amount of
oxidizing agent used can vary depending on the particular oxidizing
agent and sulfinate employed. Typically an equimolar amount or less
(based on the amount of sulfinate) is used.
[0048] Perfluorosulfinates useful for this purpose include those
described in U.S. Pat. No. 5,285,002 and represented by the general
formula:
[0049] R.sup.3.sub.fSO.sub.2M.sub.1/q
[0050] or
[0051] R.sup.2.sub.f[SO.sub.2M.sub.1/q].sub.j
[0052] where:
[0053] R.sup.3.sub.f represents a monovalent fluoroaliphatic
radical having, for example, from 1 to 20 carbon atoms, preferably
4 to 10 carbon atoms;
[0054] R.sup.2.sub.f represents a polyvalent, preferably divalent,
fluoroaliphatic radical having, for example, from 1 to 20 carbon
atoms, preferably from 2 to 10 carbon atoms;
[0055] M represents a hydrogen atom or cation with valence q, which
is 1 or 2; and j is 1 to 4, preferably 1 or 2.
[0056] The amount of fluoroaliphatic sulfinate employed in the
polymerization process can vary, depending, for example, on the
molecular weight of polymer desired. Preferably the amount of
fluoroaliphatic sulfinate is from 0.01 to 50 mole percent, and most
preferably from 0.05 to 10 mole percent, of sulfinate compound
based on total quantity of monomers.
[0057] In addition to the sulfinate, other reducing agents can be
present, such as sodium, potassium or ammonium sulfites, bisulfite,
metabisulfite, hyposulfite, thiosulfite, phosphite, sodium or
potassium formaldehyde sulfoxylate or hypophosphite. Activators
such as ferrous, cuprous, and silver salts, may also be
present.
[0058] If oil-soluble initiators are used in the polymerization, it
is generally preferred for these to be mixed with the aqueous
emulsion of the liquid perfluorovinyl ether of formula (I). For the
purpose of the present invention, oil-soluble initiators are those
which have no, or only insufficient solubility in water. Examples
include suibslituiited diel)ciizoyl peroxides, cumene
hydroperoxides, in particular bisperfluoropropionyl peroxide.
[0059] The cure site component is included in the polymerization
reaction to obtain a curable fluoroelastomer. Generally, the cure
site component will be used in small amounts, typically in amounts
so as to obtain a fluorelastomer that has between 0.1 and 5 mol %
of cure sites, preferably 0.2 to 3 mol % and most preferred 0.4-2
mol %.
[0060] The cure site component may comprise a nitrile
group-containing cure site monomer. The cure site component can be
partially or fully fluorinated. It will be understood that when the
cure site component is fully fluorinated, the resulting polymer
will be perfluorinated, and that when the cure site component is
partially fluorinated, the resulting polymer will still be highly
fluorinated. Preferred useful nitrile group-containing cure site
monomers include nitrile-containing fluorinated olefins and
nitrile-containing fluorinated vinyl ethers, such as depicted
below:
[0061] CF.sub.2.dbd.CF--CF.sub.2--O--R.sub.f--CN
[0062] CF.sub.2.dbd.CFO(CF.sub.2).sub.1CN
[0063]
CF.sub.2.dbd.CFO[CF.sub.2CF(CF.sub.3)O].sub.g(CF.sub.2O).sub.vCF(CF-
.sub.3)CN
[0064]
CF.sub.2.dbd.CF[OCF.sub.2CF(CF.sub.3)].sub.kO(CF.sub.2).sub.uCN
[0065] where, in reference to the above formulas: 1=2-12; g=0-4;
k=1-2; v=0-6; and u=1-4, R.sub.f is a perfluoroalkylene or a
bivalent perfluoroether group. Representative examples of such a
monomer include perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene),
CF.sub.2.dbd.CFO(CF.sub.2- ).sub.5CN, and
CF.sub.2.dbd.CFO(CF.sub.2).sub.3OCF(CF.sub.3)CN.
[0066] Alternatively, the cure site component may comprise a
fluorinated monomer having a halogen capable of participation in a
peroxide cure reaction. Typically the halogen is bromine or iodine.
Suitable cure-site components include terminally unsaturated
monoolefins of 2 to 4 carbon atoms such as bromodifluoroethylene,
bromotrifluoroethylene, and iodotrifluoroethylene. Examples of
other suitable cure site components include
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2Br, CF.sub.2.dbd.CFOCF.sub.2CF.su-
b.2CF.sub.2Br, and
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2OCF.sub.2CF.sub- .2Br.
Preferably, all or essentially all of these components are
ethylenically unsaturated monomers.
[0067] Still further useful cure-site components are broininated or
iodinated chain transfer agents and initiators. Examples of useful
chain transfer agents include perfluoroalkyl bromides or iodides
(see U.S. Pat. No. 4,501,869; 4,000,356). Examples of useful
initiators include X--(CF.sub.2).sub.n--SO.sub.2Na(X.dbd.Br,I CN).
Nitrile containing chain transfer agents e.g.,
1-(CF.sub.2).sub.n--CN are also useful.
[0068] When a liquid cure site monomer is used to include the cure
sites into the fluoroelastomer, it will generally be preferred that
such liquid cure site monomer is pre-emulsified, i.e. is emulsified
in water with the aid of a fluorinated emulsifier prior to its
copolyinerization. Conveniently, such liquid cure site monomer can
be pre-emulsified together with the liquid perfluorovinyl ethers of
formula (I). Pre-emulsification of the liquid cure site monomer
ensures an almost quantitive incorporation. Especially in case of
the generally expensive nitrile containing vinylethers as cure site
components it is highly desired to pre-emulsify them to ensure good
and effective incorporation.
[0069] It will be appreciated by one skilled in the art that the
pre-emulsification of liquid cure site monomers will also be
beneficial in the process of making other fluoroelastomers than
those of the present invention, which include repeating units
derived from a liquid perfluorovinyl ether of formula (I). Thus, in
a particular aspect, the present invention also provides a method
of making curable fluoroelastomers having as a cure site, a cure
site that is derived from a liquid cure site monomer, in particular
a nitrile group containing liquid cure site monomer, the method
comprising the steps of:
[0070] pre-emulsifying one or more liquid cure site monomers in
water with the aid of a fluorinated emulsifier to obtain an aqueous
emulsion
[0071] and copolymerizing the pre-emulsified liquid cure site
monomers with one or more gaseous fluorinated monomers.
[0072] Suitable gaseous fluorinated monomers include those
mentioned above as well as vinylidenefluoride.
[0073] To cure fluoroelastomers that include a halogen capable of
participation in a peroxide cure reaction, peroxides are used to
cure the fluoroelastomer. Suitable peroxide curatives are those
which generate free radicals at curing temperatures. A dialkyl
peroxide or a bis(dialkyl peroxide) which decomposes at a
temperature above 50.degree. C. is especially preferred. In many
cases it is preferred to use a di-tertiarybutyl peroxide having a
tertiary carbon atom attached to peroxy oxygen. Among the most
useful peroxides of this type are
2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexyne-3 and
2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexane. Other peroxides can
be selected from such compounds as dicumyl peroxide, dibenzoyl
peroxide, tertiarybutyl perbenzoate,
.alpha.,.alpha.'-bis(t-butylperoxy-diisopropyl- benzene), and
di[1,3-dimethyl-3-(t-butylperoxy)-butyl]carbonate. Generally, about
1-3 parts of peroxide per 100 parts of perfluoroelastomer is
used.
[0074] Another material which is usually blended with the
composition as a part of the curative system is a coagent composed
of a polyunsaturated compound which is capable of cooperating with
the peroxide to provide a useful cure. These coagents can be added
in an amount equal to 0.1 and 10 parts per hundred parts
perfluoroelastoiner, preferably between 2-5 parts per hundred parts
fluoroelastomer. Examples of useful coagents include triallyl
cyanurate; triallyl isocyanurate; tri(methylallyl isocyanurate;
tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallyl
acrylamide; hexaallyl phosphoramide; N,N,N',N'-tetraalkyl
tetraphthalamide; N,N,N',N'-tetraallyl malonamide; trivinyl
isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and
tri(5-norbornene-2-methylene)cyanur- ate. Particularly useful is
triallyl isocyanurate. Other useful coagents include the
bis-olefins disclosed in EPA 0 661 304 A1, EPA 0 784 064 A1 and EPA
0 769 521 A1.
[0075] When the fluoroelastomer includes a nitrile containing cure
site component, a catalyst comprising one or more
ammonia-generating compounds may be used to cause curing.
"Ammonia-generating compounds" include compounds that are solid or
liquid at ambient conditions but that generate ammonia under
conditions of cure. Such compounds include, for example,
hexamethylene tetramine (urotropin), dicyan diamid, and
metal-containing compounds of the formula:
[0076] A.sup.w+(NH.sub.3).sub.vY.sup.w-
[0077] where A.sup.w+ is a metal cation such as Cu.sup.2+,
Co.sup.2+, Co.sup.3+, Cu.sup.+, and Ni.sup.2+; w is equal to the
valance of the metal cation; Y.sup.w- is a counterion, typically a
halide, sulfate, nitrate, acetate or the like; and v is an integer
from 1 to about 7.
[0078] Also useful as ammonia-generating compounds are substituted
and unsubstituted triazine derivatives such as those of the
formula: 2
[0079] wherein R is a hydrogen or a substituted or unsubstituted
alkyl, aryl, or aralkyl group having from 1 to about 20 carbon
atoms. Specific useful triazine derivatives include
hexahydro-1,3,5-s-triazine and acetaldehyde ammonia trimer.
[0080] The fluoroelastomers including a nitrile containing cure
site component can also be Cured using one or more peroxide
curatives along with the ammonia generating catalysts. Suitable
peroxide curatives for this purpose include those listed above. It
will further be understood by one skilled in the art that the
curable fluoroelastomer may include a mixture of cure site
components, such as a mixture of nitrile containing cure sites and
Cure sites including a halogen capable of participating in a
peroxide cure reaction. In the latter case, a mixture of ammonia
generating compounds and peroxides will generally be employed.
[0081] To cure the nitrile containing perfluoroelastomers all other
well-known compounds can be used, like amino phenols (U.S. Pat. No.
5,677,389), ammonia salts (U.S. Pat. No. 5,565,512), amidoxinies
(U.S. Pat. No. 5,668,221) and other ammonia generating comp (PCT
00/09603).
[0082] The curable fluoroelastomer obtained by the process of the
present invention can be used to prepare a curable fluoroelastomer
composition. Such composition will generally include the curable
fluoroelastoiner and one or more curiatives such as the peroxide
and/or one or more catalysts such ammonium generating compounds
depending on the type of cure sites contained in the curable
fluoroelastomer. Additives, such as carbon black, stabilizers,
plasticizers, lubricants, fillers, and processing aids typically
utilized in fluoroelastomer compounding can be incorporated into
the compositions, provided they have adequate stability for the
intended service conditions.
[0083] Carbon black fillers are typically also employed in
clastoiiicirs as a means to balance modulus, tensile strength,
elongation, hardness, abrasion resistance, conductivity, and
processability of the compositions. Suitable examples include MT
blacks (medium thermal black) designated N-991, N-990, N-908, and
N-907, and large particle size furnace blacks. When used, 1-70 phr
of large size particle black is generally sufficient.
[0084] Fluoropolymer fillers may also be present in the curable
compositions. Generally, from 1 to 50 parts per hundred
fluoroelastomer of a fluoropolymer filler is used. The
fluoropolymer filler can be finely divided and easily dispersed as
a solid at the highest temperature utilized in fabrication and
curing of the fluoroelastomer composition. By solid, it is meant
that the filler material, if partially crystalline, will have a
crystalline melting temperature above the processing temperature(s)
of the fluoroelastomer(s). The most efficient way to incorporate
fluoropolymer filler is by blending latices; this procedure
including various kinds of fluoro polymer filler is described in
U.S. application No. 09/495600, filed Feb. 1, 2000.
[0085] One or more acid acceptors can also be added to the curable
composition, though, where the presence of extractable metallic
compounds is undesirable (such as for semiconductor applications)
the use of inorganic acid acceptors should be minimized, and
preferably avoided altogether. Commonly used acid acceptors
include, for example, zinc oxide, calcium hydroxide, calcium
carbonate, magnesium oxide, etc. These compounds generally are used
in the fluoroelastomer formulation to bind any HF or other acids
that might be generated at the high temperatures where
fluoroelastomers must function.
[0086] The curable compositions can be prepared by mixing the
fluoroelastomer, the curatives and/or catalysts, the selected
additive or additives, and the other adjuvants, if any, in
conventional rubber processing equipment. The desired amounts of
compounding ingredients and other conventional adjuvants or
ingredients can be added to the unvulcanized fluorocarbon gum stock
and intimately admixed or compounded therewith by employing any of
the usual rubber mixing devices such as internal mixers, (e.g.,
Banbury mixers), roll mills, or any other convenient mixing device.
For best results, the temperature of the mixture during the mixing
process typically should not rise above about 120.degree. C..
During mixing, it is preferable to distribute the components and
adjuvants uniformly throughout the gum for effective cure. The
mixture is then processed and shaped, for example, by extrusion
(for example, in the shape of a hose or hose lining) or molding
(for example, in the form of an O-ring seal). The shaped article
can then be heated to cure the gum composition and form a cured
elastomer article.
[0087] Processing of the compounded mixture (i.e., press cure)
usually is conducted at a temperature between about 95.degree. C.
and about 230.degree. C., preferably between about 150.degree. C.
and about 205.degree. C., for a period of from 1 minute to 15
hours, typically from 5 minutes to 30 minutes. A pressure of
between about 700 kPa and about 20,600 kPa is usually imposed on
the compounded mixture in the mold. The molds first may be coated
with a release agent and prebaked. The molded vulcanizate is then
usually post-cured (e.g., oven-cured) at a temperature usually
between about 150.degree. C. and about 300.degree. C., typically at
about 232.degree. C., for a period of from about 2 hours to 50
hours or more depending on the cross-sectional thickness of the
article. For thick sections, the temperature during the post cure
is usually raised gradually from the lower limit of the range to
the desired maximum temperature. The maximum temperature used is
preferably about 300.degree. C., and is held at this value for
about 4 hours or more.
[0088] The curable compositions are useful in production of
articles such as gaskets, tubing, and seals. Such articles are
produced by molding a compounded formulation of the curable
composition with various additives under pressure, curing the part,
and then subjecting it to a post cure cycle. The curable
compositions formulated without inorganic acid acceptors are
particularly well suited for applications such as seals and gaskets
for manufacturing semiconductor devices, and in seals for high
temperature automotive uses.
[0089] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of the present invention, and it should be
understood that this invention is not to be unduly limited to the
illustrative embodiments set forth herein.
EXAMPLES
[0090] The following abbreviations are used in the examples:
[0091] AFPO: Ammonium-perfluoro octanoate
[0092] MV31: CF.sub.2.dbd.CFO(CF.sub.2).sub.3OCF.sub.3
[0093] MV21: CF.sub.2.dbd.CFO(CF.sub.2).sub.2OCF.sub.3
[0094] TFE: tetrafluoroethylene
[0095] BTFE: Bromotrifluoroethylene
[0096] CSM: cure site monomer
[0097] APS: Ammonium persulfate
[0098] PMVE: perfluoro methyl vinylether
[0099] PVE: emulsified perfluoro vinylether 3
[0100] Test methods
[0101] In the following examples, indicated results were obtained
using the following test methods:
[0102] Cure rheology: Cure rheology tests were run on uncured,
compounded samples using a Goettfert Elastograph 67.85 in
accordance with ASTM D 5289-93a at 170 .degree. C., no pre-heat, 12
minute elapsed time, and a 0.2 degree arc. Both the minimum torque
(M.sub.L) and highest torque attained during a specified period of
time when no plateau or maximum torque was obtained (M.sub.H) were
measured. Also measured were the time for the torque to increase 2
units above M.sub.L ("t.sub.s2") the time for the torque to reach a
value equal to M.sub.L+0.5(M.sub.H-M.sub.L) ("t'50), and the time
for the torque to reach M.sub.L+0.9(M.sub.H-M.sub.L- )
("t'96").
[0103] Press-Cure samples: Unless otherwise noted,
150.times.150.times.2.0 mm sheets were prepared for physical
property determination by pressing at about 6.9 Mega Pascals (MPa)
for 30 minutes at 177 .degree. C.
[0104] Tensile Strength at Break, Elongation at Break and Modulus
at 100% Elongation were determined using ASTM D 412-92 on samples
cut from the press-cure or post-cure sliect with ASTM Die D.
[0105] Hardness was determined using ASTM D 2240-85 Method A with a
Type A-2 Shore Durometer. Units are reported in points.
[0106] Compression set was determined on O-rings using ASTM 395-89
Method B. The O-rings had a cross-section thickness of 0.139 in.
(3.5 mm).
[0107] Glass transition temperatures were measured by DSC according
ISO 12086.
[0108] Mooney viscosities was measured according ASTM D 1646.
[0109] Preparation of the perfluoro vinylether pre-emulsion
[0110] The liquid perfluoro vinylether is emulsified in water
according to the following procedure: 500 g of the perfluoro
vinylether and 500 g of deionized water containing 3 g APFO are
emulsified with an "Ultra Turrax"-device (IKA Turrax T25S25N186) at
a speed of 24000 rpm for 1 minute under a N.sub.2-blanket. A
milky-white emulsion is obtained having a pot life of at least 3
hours. The O.sub.2-free perfluoro vinyl ether emulsion was then fed
into the polymerization vessel.
Example 1
[0111] A 4 1-vessel was charged with 2.8 1 0.sub.2-free water
containing 10 g APFO and 8 g ammonia-oxalate. Additionally 150 g MV
31 pre-emulsified in water, 3 g BTFE and 180 g TFE were added and
the polymerization was initiated at 60.degree. C. by adding 30 ml
of 0.2% KMnO.sub.4-solution. The polymerization was continued at
60.degree. C. and 9 bar pressure for 5 h, during this time 0.6 g
KMnO.sub.4, 8 g BTFE, 550 g TFE and 600 g MV 31 pre-emulsified in
water were continuously added. The clear latex was coagulated by
adding MgCl.sub.2-solution, the washed gum was dried at 130.degree.
C. The resulting polymer has T.sub.G of -23.degree. C., a Mooney
value of 70 and consists of 76.9 mol-% TFE, 22.5 mol-% MV 31 and
0.6 mol-% BTFE.
Examples 2 to 7
[0112] The fluoroelastomers of examples 2 to 7 were prepared
according to the polymerization method described in example 1 but
with the exception that the monomers and amounts as indicated in
table 1 were used.
[0113] Cure Properties
Example 3
[0114] 100 Parts of Example 3 were compounded with 15 parts carbon
black MT N990 and 1 part Urotropin (hexamethylene tetramine). A
sheet of the compounded mixture was pressed for 30 minutes at
177.degree. C. and then subsequently post-cured under nitrogen
using the following conditions: 25-200.degree. C. in 16 hrs.,
200.degree. C. for 16 hrs, 200.degree. C.-250.degree. C. in 2 hrs,
250.degree. C. for 8 hrs, 250.degree. C.-300.degree. C. in 2 hrs
and 300.degree. C. for 16 hrs. The cured samples were tested to the
indicated test methods, giving the following results:
1 Tensile strength 2,240 psi 15.45 MPa Elongation 160% 100% Modulus
1080 psi 7.45 MPa Shore A Hardness 78
[0115] Cure Properties
Examples 4, 5, 7
[0116] 100 parts of the peroxide curable materials containing BTFE
were compounded with 20 parts MT N-990, 2.50 parts ZnO, 1.35 parts
Trigonox 101-50D, 3.50 parts Perkalink 301-50D and 1 part Struktol
WB-222. The compounded materials show for example the following
cure characteristics (Goettfert Elastograph 67.85):
2 MDR 170.degree. C. (50 cpm, 0.2.degree. ARC) Example 4 Example 5
Example 7 ML (Nm) 0.09 0.09 0.09 MH (Nm) 0.95 0.90 0.85 Ts2 (min)
0.6 0.6 0.7 Tc50 (min) 1.2 1.2 1.4 Tc90 (min) 3.4 3.2 3.5 Vmax
(Nm/min) 0.69 0.66 0.55
[0117] Sheets were pressed from materials of Ex. 4, 5 and 7
press-cured for 10 min at 170.degree. C. and post cured for 16 hrs
at 230.degree. C. The following properties were measured:
3 Example 4 Example 5 Example 7 Tensile strength (MPa) 15.7 13.2
14.6 Elongation 130 125 125 100% Modulus 11.4 10.0 14.6 Shore A
Hardness 77 73 84 Compression set 22 23 28 (70 hrs at 200.degree.
C.)
[0118]
4 Composi- Pre- PVE Gaseous Polym. tion charges Mono- Mono- Polym.
Pres- Run (mol %) Moo TFE/PMVE/ mer CSM mers Initiator Temp. sure
Time TFE/PMVE/ T.sub..OMEGA. ncy Ex PVE/CSM (g) (g) (g) (g)
(.degree. C.) (bar) (h) PVE/CSM (.degree. C.) Value 2 TFE:120 g MV
BTFE TFE KMnO.sub.4 50 6 4.2 71/28/1 -27 60 PVE:120 g 31 (10) (390)
(0.8) CSM: 3g (745) 3 TFE:190 MV CN TFE KMnO.sub.4 60 9 7.5
77/-/22/1 -23 55 PVE:200 31 31 (600) (0.4) CSM:10 (590) (33) 4
TFE:175 MV BTFE TFE KMnO.sub.4 50 9 5.3 73/9/17/1 -16 70 PMVE:60 31
10 (550) (0.4) PVE:180 (480) PMVE CSM:4 (130) 5 TFE.150 MV BTFE TFE
KMnO.sub.4 50 9 5 68/12/19/1 -19 60 PMVE:120 31 10 500 0.9 PVE:200
580 PMVE CSM:4 160 6 TFE:140 MV BTFE TFE APS 70 9 4 751-124/1 -11
45 PVE:350 21 (10) (400) (3) CSM:3 (670) 7 TFE:180 MV BTFE TFE
KMnO.sub.4 63 9 5 78/21/1 -20 55 PVE:160 31 10 600 0.4 CSM:3
550
Comparative Example 1
[0119] A 4 1-vessel was charged with 2.8 1 O.sub.2-free water
containing 15 g APFO. 100 g TFE, 205 g PMVE and 7 g liquid CSM
4
[0120] were added, the polymerization was initiated at 68.degree.
C. by adding 5 g APS. The polymerization was tinued at 68.degree.
C. and 12 bar pressure for 5.8 h during this time 550 g TFE, 475
PMVE 67 g liquid CSM were continuously added. The resulting polymer
showed by IR.sup.- and NMR-analysis an incorporation of 1.1 mol
CSM.
[0121] The polymerization was repeated, but pre-emulsified CSM was
used, to obtain the same incorporation (1.1 mol %) in total only 44
g pre-emulsified CSM (5 g pre-emulsified CSM as precharge, 39 g
pre-emulsified CSM was added during the course of polymerization)
was necessary.
[0122] By using pre-emulsification technique less than 40% of
liquid CSM is required to obtain the same incorporation.
Comparative Example 2
[0123] Example 2 was repeated under identical conditions, except
that all the MV31 was not pre-emulsified. The resulting reaction
mixture shows 2 phases, the lower phase is unreacted MV31 and the
upper phase consists of a polymer which has only 13 mol % MV31
incorporated.
* * * * *